Integrated endpoint detection system with optical and eddy current monitoring

Abstract

A chemical mechanical polishing apparatus and method can use an eddy current monitoring system and an optical monitoring system. Signals from the monitoring systems can be combined on an output line and extracted by a computer. A thickness of a polishing pad can be calculated. The eddy current monitoring system and optical monitoring system can measure substantially the same location on the substrate.

1. A method of measuring conductive layer thickness during chemical mechanical polishing, the method comprising:
 positioning a substrate having a conductive layer disposed thereon in contact with a polishing surface of a polishing pad; 
 creating relative motion between the substrate and the polishing pad to polish the substrate; 
 driving an inductor with a drive signal to generate an alternating magnetic field that induces eddy currents in the conductive layer during polishing; 
 measuring a strength of the magnetic field and a phase difference between the magnetic field and the drive signal during polishing; 
 calculating a correction factor based on the strength of the magnetic field; 
 calculating a thickness of the conductive layer from the phase difference and the correction factor; and 
 polishing a test substrate with a first polishing pad having a first known thickness and with a second polishing pad having a second known thickness, and generating at least one coefficient to relate pad thickness to magnetic field strength during polishing; and 
 calculating the thickness of the polishing pad contacting the substrate from at least the strength of the magnetic field and the coefficient. 
 
   
   
     2. A method of measuring conductive layer thickness during chemical mechanical polishing, the method comprising:
 positioning a substrate having a conductive layer disposed thereon in contact with a polishing surface of a polishing pad; 
 creating relative motion between the substrate and the polishing pad to polish the Substrate; 
 driving an inductor with a drive signal to generate an alternating magnetic field that induces eddy currents in the conductive layer during polishing; 
 measuring a strength of the magnetic field and a phase difference between the magnetic field and the drive signal during polishing; 
 calculating a correction factor based on the strength of the magnetic field; 
 calculating a thickness of the conductive layer from the phase difference and the correction factor; 
 polishing a test substrate with a first polishing pad when the first polishing pad has a first known thickness, polishing the test substrate with the first polishing pad when the first polishing pad has a second known thickness, and generating at least one coefficient to relate pad thickness to magnetic field strength during polishing; and 
 calculating the thickness of the polishing pad contacting the substrate from at least the strength of the magnetic field and the coefficient. 
 
   
   
     3. The method of  claim 2 , further comprising alerting a user if the thickness of the polishing pad contacting the substrate falls below a predetermined thickness. 
   
   
     4. A computer-program product, tangibly stored on machine readable medium, the product comprising instructions operable to cause a polisher to perform a method comprising:
 positioning a substrate having a conductive layer disposed thereon in contact with a polishing surface of a polishing pad; 
 creating relative motion between the substrate and the polishing pad to polish the substrate; 
 driving an inductor with a drive signal to generate an alternating magnetic field that induces eddy currents in the conductive layer; 
 measuring a strength of the magnetic field and a phase difference between the magnetic field and the drive signal; 
 calculating a correction factor based on the strength of the magnetic field; and 
 calculating a thickness of the conductive layer from the phase difference and the correction factor; 
 polishing a test substrate with a first polishing pad having a first known thickness and with a second polishing pad having a second known thickness, and generating at least one coefficient to relate pad thickness to magnetic field strength during polishing; and 
 calculating the thickness of the polishing pad contacting the substrate from at least the strength of the magnetic field and the coefficient. 
 
   
   
     5. A computer-program product, tangibly stored on machine readable medium, the product comprising instructions operable to cause a polisher to perform a method comprising:
 positioning a substrate having a conductive layer disposed thereon in contact with a polishing surface of a polishing pad; 
 creating relative motion between the substrate and the polishing pad to polish the substrate; 
 driving an inductor with a drive signal to generate an alternating magnetic field that induces eddy currents in the conductive layer; 
 measuring a strength of the magnetic field and a phase difference between the magnetic field and the drive signal; 
 calculating a correction factor based on the strength of the magnetic field; and 
 calculating a thickness of the conductive layer contacting the substrate from the phase difference and the correction factor; 
 polishing a test substrate with a first polishing pad when the first polishing pad has a first known thickness, polishing the test substrate with the first polishing pad when the first polishing pad has a second known thickness, and generating at least one coefficient to relate pad thickness to magnetic field during polishing; and 
 calculating the thickness of the polishing pad contacting the substrate from at least the strength of the magnetic field and the coefficient. 
 
   
   
     6. The product of  claim 5 , wherein the method further comprises providing an alert if the thickness of the polishing pad contacting the substrate falls below a predetermined thickness.